Method and apparatus for improved transfer of heat

ABSTRACT

Disclosed are a method for improving the heat transfer characteristics of a heat exchanger and a heat exchanger structure capable of operating in accordance with the method. The disclosed method comprises causing a heat exchange medium to flow alternately through two different types of zones. In the first zone the flow patterns developed in the fluid are generally translatory while in the second zone the patterns are generally rotational. The heat exchange fluid is caused to flow at least partly across the heat exchange surface while in the second zone. In the apparatus, the zones are presented as compartments divided by a wall, one of the compartments being at least partially bounded by the heat exchange surface. The medium flows in a translatory manner through one compartment and through a conducting device which interconnects the compartments. A rotational movement is imparted on the fluid flowing into the other compartment.

United States Patent [1 1 Lage [ Nov. 13, 1973 METHOD AND APPARATUS FOR IMPROVED TRANSFER OF HEAT [76] Inventor: James Richard Lage, Umiken,

Switzerland [22] Filed: Nov. 1, 1971 [21] Appl. No.: 194,282

[30] Foreign Application Priority Data FOREIGN PATENTS OR APPLICATIONS 1,108,372 6/1961 Germany 165/1 Primary Examiner-Manuel A. Antonakas Att0rneyWatson, Cole, Grindle & Watson 5 7] ABSTRACT Disclosed are a method for improving the heat transfer characteristics of a heat exchanger and a heat exchanger structure capable of operating in accordance with the method. The disclosed method comprises causing a heat exchange medium to flow alternately through two different types of zones. In the first zone the flow patterns developed in the fluid are generally translatory while in the second zone the patterns are generally rotational. The heat exchange fluid is caused to flow at least partly across the heat exchange surface while in the second zone. In the apparatus, the zones are presented as compartments divided by a wall, one of the compartments being at least partially bounded by the heat exchange surface. The medium flows in a translatory manner through one compartment and through a conducting device which interconnects the compartments. A rotational movement is imparted on the fluid flowing into the'other compartment.

19 Claims, 6 Drawing Figures Patented Nov. 13, 1973 METHOD AND APPARATUS FOR IMPROVED TRANSFER OF HEAT CROSS REFERENCE TO RELATED APPLICATION Applicant claims priority from corresponding Swiss Patent Application Ser. No. 016,708/70 filed Nov. 10, 1970.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for improving the heat transfer characteristics of an indirect heat exchanger and an exhanger constructed to carry out the process.

2. Description of the Prior Art In many previously known indirect heat transfer applications, including either delivery of heat or heat absorption processes, the heat transfer medium is usually directed to flow in a generally unconstrained manner across the heat transfer surface, whereby the medium follows a substantially uncontrolled, nearly random flow path across the surface. In such instances the path of least resistance is taken by the fluid and in most instances this is also the shortest path. Accordingly, most of the individual particles of the medium traverse the heat transfer surface only once. Moreover, it is extremely rare under such circumstances for any individual particle of heat transfer medium to contact the entirety of a heat exchange surface. As a result, low heat transfer coefficients are developed.

SUMMARY OF THE INVENTION The primary object of the present invention is to provide a heat transfer method and apparatus which facilitate the longest possible contact between the particles of the heat transfer medium and the heat transfer surface whereby a high heat transfer coefficient results. This result is obtained by causing the particles of the medium to flow across the heat transfer surface in an aligned, forced flow path.

The desired results are achieved, according to the invention, by developing alternating flow patterns in the medium which is guided essentially translatorily in a first zone and rotatingly in a second zone. The medium is conducted at least partially along the heat exchange surface in the second zone.

According to a preferred embodiment of the process, the medium in the second zone is caused to traverse a spiral path. A further advantageous feature of the invention consists in causing only a part of the medium to traverse the entire helical path while remaining parts of the medium are fed in at downstream locations to traverse only the remainder of the path.

A heat exchanger adapted to carry out the process has a housing defining a chamber which is subdivided into first and second flow compartments. The second compartment is bounded at least partially by the heat exchange surface. The exchanger is provided with an inlet communicating with the first chamber and an outlet communicating with the second chamber. Medium under pressure is supplied to the first flow chamber, and a conducting device which intercommunieates the compartments and directs fluid flowing therethrough into the second flow compartment in at least one essentially translatory jet. The conducting device is also disposed and arranged to cause the medium to flow rotatingly through said second compartment. The term translatory flow as used herein designates a flow in which the medium traverses substantially the shortest path and flows generally in a single direction, for example, as through a space, pipe or nozzle.

In the second zone, the medium does not flow over the direct and shortest path, but rather, it is subjected to a rotating flow. The term rotating flow, as used herein, designates a flow which circulates around an axis, such as for example, a pulsating flow, a rotating or a twisting flow, a rolling movement of the medium, as well as combinations of these. If at the same time an additional secondary forward movement, preferably in the axial direction is imparted to the medium, then the particles of the medium will follow a generally helical path. In this manner the medium may form a roller progressing through the flow chamber in an axial direction.

The cross section of the roller does not need to be circular, for example in the case where the flow chamber is rectangular, and its diameter can change along the axis.

A considerably greater heat transfer coefficient can be achieved in the case of a purely rotating flow than in the case of translatory flow, resulting from improved intermixture of the medium. A still further increase in the magnitude of heat transfer coefficient can be achieved through the establishment of a helical flow path. With helical flow paths, multiple sweeps of the medium across the heat exchange surface provide a better utilization of the available heat transfer surface. The method and apparatus of the present invention may be utilized with all fluid mediums, whether gases or liquids, or condensing or evaporating fluids.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view diagrammatically illustrating the basic concepts and principles of the invention;

FIG. 2 is an elevational, cross sectional view of an exchanger which embodies the principles and concepts of the invention and has several chambers arranged in series;

FIG. 3 is an enlarged, cross sectional view taken substantially along line IIIIII of FIG. 2;

FIG. 4 is a cross sectional view taken substantially along line IVIV of FIG. 3;

FIG. 5 is a cross sectional view similar to FIG. 3 illustrating another embodiment of this invention; and

FIG. 6 is a cross sectional view taken substantially along line VIVI of FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The individual steps in the process are illustrated in FIG. 1 wherein translatory flows are designated by the reference numeral 1 and rotating flows are designated by the numeral 2. The flowing medium is first conducted translatorily in a first zone and as a result, its

flow paths are aligned and uniform. Thereafter, the medium is directed, preferably with an increased speed and after the necessary deflections, into a second zone and into contact with a heat exchange surface 4, at any desired angle or even parallel to surface 4, whereby the flow 2 is deflected and put into rotation. Preferably, an axial flow direction will also be imparted upon the rotating flow, and as a result, the path of flow 2 becomes helical. At the same time, depending upon the construction of the, exchanger, the medium may be conducted continuously or with interruptions along heat exchange surface 4.

During helical flow, the larger the peripheral component of the flow relative to its axial component, the larger the number of surface segments of the heat exchange surface which will be contacted by any individual particle of the medium. correspondingly heat transfer will be made more efficient and the utilization of the heat exchange surface will be improved. It has been found to be advantageous to utilize the highest speed of flow on the helical path and that the circumferential speed of the medium at the outer peripheral portions of the continuously moving roller thereof should be at least about 7r times the linear axial speed of the medium. It should be appreciated, also, that the translatory flow in the first zone could be advantageously conducted across the heat exchange surface. However, this is not essential to the present invention.

It has been found also that better utilization of the heat transfer surface and an improved effect can be achieved whenever the heat exchange surface is contacted by a large number of small helical flows each of which comprises merely a portion of the medium rather than by a single helical flow which includes all of the medium.

In order to achieve maximum intermixture of the particles of the medium and thus provide substantial uniformity of temperature in the medium whereby to eliminate temperature gradients and improve heat exchange characteristics, medium can be fed into the second zone at various locations along the helical path and as a result, friction losses and the resultant lowering of speed are decreased. Manifestly, to obtain any desired, predetermined temperature drop, it may be necessary to repeat the traversing of the zones. In such case the flow again is stabilized and aligned in a first zone and is again caused to rotate in the second zone. Assuming a continuous supply of the medium, the flow in all zones is stable and the manner and form of the flow paths remain constant.

The exchanger illustrated in FIG. 2 consists of four individual chambers 3 which have been combined into one unit although each would be fully operable by itself. Pressurized medium enters the righthand side of the installation and flows through in the direction of the arrow. Each chamber 3 is divided into a first flow compartment 9 and a second flow compartment by separating means in the nature of a wall 5 which has a lower edge portion 12 adjoining heat exchange surface 4. Wall 5 extends angularly upwardly relative to the general direction of the flow in the exchanger. The medium entering the first flow chamber 9 is guided upwardly and laterally along separating wall 5 to a gap 7 (FIGS. 3 and 4) defined by a side wall 8 of chamber 3 and a wall 6 which extends downwardly from separating wall 5. Wall 6, which may be integral with wall 5, extends toward surface 4 and terminates in spaced relationship thereto presenting an opening 11 through which the medium flows in a jet into the second flow compartment.

The medium is introduced into the second flow compartment in the direction of heat exchange surface 4 and it is deflected by said surface and put in rotation. Thus, the medium is caused to flow in a helical path 2 (FIG. 4) which moves according to FIG. 2 from right to left. Because of the angular disposition of separating wall 5, the rotating paths 2 continuously increase in di ameter along the axial direction. Because gap 7 extends along the entire length of chamber 3, fresh medium and thus new energy is continuously introduced in the second flow compartment at various locations along the helical path.

Separating wall 5 could be disposed parallel to heat exchange surface 4, which, from a constructional point of view, would be simpler; however, with regard to proper flow characteristics and to an efficient utilization of heat exchange surface, this would be less favorable than the configuration shown.

By utilizing a direct series connection of several chambers with a direct flow of medium emerging from one of the chambers entering into the next, it will be possible to achieve the lowest frictional pressure losses and a compact constructional size. Alternatively, it might be desirable for the medium to traverse the same chamber several times and for this purpose a pumping device could be connected into the system to recirculate the medium.

FIGS. 5 and 6 illustrate another embodiment of the exchanger. In this case, gap 7 is disposed in the center of chamber 3, and the medium flows in from both sides along the paths 1. With this arrangement, two rotating paths 2 will develop (FIG. 6) at the sides of gap 7 in a second flow compartment 10'divided in such a way. The advantage of this embodiment is of a constructional nature, consisting primarily in the fact that a more compact and symmetrical type of construction will be possible.

It should be appreciated that a gap similar to gap 7 could be provided at each side of the chamber and for that matter, several such gaps could be distributed over the width of the chamber. In such cases, the rotating flows would touch each other but they should still be able to develop inspite of this. Furthermore, the gaps could decrease in flow area as the second compartment is approached, for example, through a convergence of surfaces 6 or 8 or by providing a nozzle at opening 11, whereby the medium would be accelerated as it passes into compartment 10. The maximum speed should occur as the medium enters the second compartment 10. To further enhance the development of a rotating flow, wall 6 can be provided with a flange portion 13 (indicated in FIGS. 4 and 6 by a dashed line) which is disposed adjacent opening 11 and extends generally parallel to surface 4. As a result, the medium flows into the second flow compartment 10 in a direction parallel to heat exchange surface 4.

The development of a rotating flow also can be enhanced by the provision of a heat exchange surface having a curvature. In an extreme form, the chamber could be cylindrical. Also, the heat exchange surface could be curved to present a convex surface in the second compartment if this would prove to be advantageous or if the shape of the heat exchange surface is determined by other considerations. Furthermore, the axis of the helical path could be curved if, for example, an elongated shape of the successive chambers must be avoided. Obviously identical chambers could be disposed on opposite sides of the heat exchange surface.

As illustrated in FIGS. 2, 3 and 4, gap 7, which is defined between walls 6 and 8, presents a conducting device which intercommunicates compartments 9 and 10. Instead of wall 6, the conducting device could comprise, especially if chamber 3 is not very high, several openings in separating wall 5. The openings could be round, oval or any other shape. Further, the openings could be disposed in a continuous row or replaced by an elongated slit. A pipe could be utilized to convey fluid from each opening. Preferably such pipe should be of the same shape as its opening and should extend toward the heat exchange surface. Each pipe may be bent at its free end in order to achieve a similar effect to that achieved with flange 13 of limiting wall 6. Separating wall 6 can be parallel to heat exchange surface 4 or it can approach it in the flow direction and as a result of the latter, the diameter of the helical rotating path would decrease along the axis of the compartment.

Walls swept by medium but which are not integral parts of the heat exchange surface, such as, for example, the lateral walls 8 of chamber 3, may advantageously be connected to the heat exchange surface in a heat conductive manner. Ribs may be provided for the same purpose. Such ribs may be disposed to extend in the direction of the helical path of the medium and should be connected to the heat exchange surface and- /or the lateral walls of the chamber in a heat conducting manner.

I claim:

1. A heat exchanger comprising:

a housing defining a chamber;

means in said housing dividing said chamber into first and second compartments, there being an inlet communicating with said first compartment and an outlet communicating with said second compartment,

said housing including a heat exchange surface which at least partially bounds said second compartment, said means comprising a separating wall having a lower edge portion adjoining said heat exchange surface and slanting upwardly toward the upper portion of said housing in the direction of flow of a medium through said chamber,

said inlet being disposed to direct a flow of the heat exchange medium through said first chamber in a generally translatory stream; and

conducting device on said dividing wall intercommunicating the compartments, said device being disposed for directing the flow of medium into said second compartment and causing it to rotate therein.

2. An exchanger as set forth in claim 1 wherein the separating wall has a portion comprising a limiting wall partially defining a nozzle like gap which is directed toward the second flow chamber and presents said conducting device.

3. An exchanger as set forth in claim 2 wherein said limiting wall defining the gap terminates in spaced relationship to the heat exchange surface presenting an opening for the conducting device through which the medium flows into the second compartment.

4. An exchanger as set forth in claim 3 wherein said limiting wall extends generally perpendicularly toward the heat exchange surface and has a flange portion adjacent said opening extending generally parallel to the heat exchange surface.

5. An exchanger as set forth in claim 1 wherein said wall has at least one opening for the medium therein presenting said conducting device.

6. An exchanger as set forth in claim 5 wherein said opening has the configuration of an elongated slit.

7. An exchanger as set forth in claim 5 wherein said conducting device comprises a pipe communicating with each opening and directed toward the heat exchange surface.

8. An exchanger as set forth in claim 7 wherein the pipe is bent at its end adjacent the heat exchange surface.

9. An exchanger as set forth in claim 1 wherein the heat exchange surface is curved. 10. A process for improving the heat transfer capabilities in an indirect heat exchange apparatus having a heat exchange surface over which a heat exchange medium flows, said process comprising:

supplying a pressurized flow of heat exchange medium to said apparatus from a source of supply thereof;

directing said medium through a first zone in said apparatus and maintaining the flow characteristics of the medium generally translatory while in said first zone; and

conducting said medium through a second zone in said apparatus and causing said medium to flow in rotational patterns while in said second zone with said patterns traversing a pyramidal helical path between asmall and a larger end while in said second zone, said medium being directed to flow at least partly across said heat exchange surface while in said second zone.

11. A process as set forth in claim 10 wherein the axis of the helical path is curved.

12. A process as set forth in claim 10 wherein only a part of the medium traverses the entire helical path while in the second zone and the remainder of the medium is fed in downstream and traverses only a portion of the path.

13. A process as set forth in claim 12 wherein the medium is fed in continuously along the entire helical 1 path.

14. A process as set forth in claim 10 wherein the translatory flow is directed angularly toward the heat exchange surface.

15. A process as set forth in claim 10 wherein the rotational speed of the medium in the second zone is at least equal to the highest translatory flow speed in the first zone.

16. A process as set forth in claim 10 wherein the velocity of the medium flowing from the first zone into the second zone is accelerated by passing through nozzle shaped areas flow restricting.

17. A process as set forth in claim 10 wherein the highest flow speed on the helical path in the second zone is at least '11 times as great as the axial speed of the medium.

18. A process as set forth in claim 10 wherein the medium traverses each zone several times.

19. A process as set forth in claim 10 wherein the medium traverses a plurality of first and second zones alternately. 

1. A heat exchanger comprising: a housing definiNg a chamber; means in said housing dividing said chamber into first and second compartments, there being an inlet communicating with said first compartment and an outlet communicating with said second compartment, said housing including a heat exchange surface which at least partially bounds said second compartment, said means comprising a separating wall having a lower edge portion adjoining said heat exchange surface and slanting upwardly toward the upper portion of said housing in the direction of flow of a medium through said chamber, said inlet being disposed to direct a flow of the heat exchange medium through said first chamber in a generally translatory stream; and conducting device on said dividing wall intercommunicating the compartments, said device being disposed for directing the flow of medium into said second compartment and causing it to rotate therein.
 2. An exchanger as set forth in claim 1 wherein the separating wall has a portion comprising a limiting wall partially defining a nozzle like gap which is directed toward the second flow chamber and presents said conducting device.
 3. An exchanger as set forth in claim 2 wherein said limiting wall defining the gap terminates in spaced relationship to the heat exchange surface presenting an opening for the conducting device through which the medium flows into the second compartment.
 4. An exchanger as set forth in claim 3 wherein said limiting wall extends generally perpendicularly toward the heat exchange surface and has a flange portion adjacent said opening extending generally parallel to the heat exchange surface.
 5. An exchanger as set forth in claim 1 wherein said wall has at least one opening for the medium therein presenting said conducting device.
 6. An exchanger as set forth in claim 5 wherein said opening has the configuration of an elongated slit.
 7. An exchanger as set forth in claim 5 wherein said conducting device comprises a pipe communicating with each opening and directed toward the heat exchange surface.
 8. An exchanger as set forth in claim 7 wherein the pipe is bent at its end adjacent the heat exchange surface.
 9. An exchanger as set forth in claim 1 wherein the heat exchange surface is curved.
 10. A process for improving the heat transfer capabilities in an indirect heat exchange apparatus having a heat exchange surface over which a heat exchange medium flows, said process comprising: supplying a pressurized flow of heat exchange medium to said apparatus from a source of supply thereof; directing said medium through a first zone in said apparatus and maintaining the flow characteristics of the medium generally translatory while in said first zone; and conducting said medium through a second zone in said apparatus and causing said medium to flow in rotational patterns while in said second zone with said patterns traversing a pyramidal helical path between a small and a larger end while in said second zone, said medium being directed to flow at least partly across said heat exchange surface while in said second zone.
 11. A process as set forth in claim 10 wherein the axis of the helical path is curved.
 12. A process as set forth in claim 10 wherein only a part of the medium traverses the entire helical path while in the second zone and the remainder of the medium is fed in downstream and traverses only a portion of the path.
 13. A process as set forth in claim 12 wherein the medium is fed in continuously along the entire helical path.
 14. A process as set forth in claim 10 wherein the translatory flow is directed angularly toward the heat exchange surface.
 15. A process as set forth in claim 10 wherein the rotational speed of the medium in the second zone is at least equal to the highest translatory flow speed in the first zone.
 16. A process as set forth in claim 10 wherein the velocity of the medium flowing from the first zone into the second zone is accelerated by passing through nozzle shaped areas flow restrIcting.
 17. A process as set forth in claim 10 wherein the highest flow speed on the helical path in the second zone is at least pi times as great as the axial speed of the medium.
 18. A process as set forth in claim 10 wherein the medium traverses each zone several times.
 19. A process as set forth in claim 10 wherein the medium traverses a plurality of first and second zones alternately. 